Polymorphism of anhydrous milk fat as affected by the addition of palm stearins

Blends of anhydrous milk fat (AMF), soft palm stearin (SPOs) and hard palm stearin (HPOs) were prepared and analysed by differential scanning calorimetry (DSC) to determine their maximum melting peak temperature, Tp and melting enthalpy, ΔH and by X-ray diffractometry (XRD) to determine their polymorphism. Contour plots were produced showing the variation of Tp and ΔH with blend composition. The XRD data showed a predominance of β’ crystals and a small proportion of β crystals, both for pure AMF and SPOs, but β crystals were dominant in pure HPOs. By blending AMF with SPOs or HPOs, the polymorphic stability of β crystals increased, with the most pronounced effect being observed in the blends containing high HPOs. This was considered to be due to the enrichment of AMF with symmetrical triacylglycerols of SPOs or HPOs which reduced the chain-length diversity that was originally found in pure AMF. An exception was observed for the binary blend of 75% AMF with 25% HPOs, which indicated that the blend occurred only in β’ polymorphic form.